Vacuum treatment of molten steel is utilized in order to enhance one or more properties of the finished steel. For example, carbon removal is improved through the application of vacuum degassing without the addition of oxygen into the steel bath. However, the vacuum degassing apparatus gives a user the added option of introducing oxygen into the molten bath to form carbon monoxide which is then removed by the degassing unit. Alternatively, the steel may also be treated with one or more gases during the vacuum treatment time, and/or one or more alloying elements may also be added.
One conventional vacuum degassing process is the RH-OB system used primarily for the removal of hydrogen and/or a certain amount of carbon from the steel. The RH-OB process uses a refractory-lined vacuum vessel having two vertically depending legs or snorkels, an alloy addition hopper, a mechanism for raising and lowering the vacuum vessel into the ladle, and a steam ejector system. The RH-OB process not only introduces an inert lift gas into one of the legs through a gas inlet pipe to facilitate flow of the metal, but also gives the user the option of introducing oxygen into the molten bath when desired. The inert gas lifts the metal in the one leg and the metal leaves through the other leg, with the introduction of oxygen assisting in the decarburization of the liquid steel.
While the RH-OB process and its equipment are useful in the vacuum treatment of molten steel, a number of disadvantages have arisen because of the two legs which are immersed into the molten steel. The refractory material in the bottom section of the RH-OB vessel is complicated, expensive, and subject to rapid wear. The snorkels may plug, and maintenance of the snorkels and the vessel bottom is correspondingly difficult.
Those skilled in the art will understand that there is a need for a method and apparatus for vacuum treating molten steel which overcomes the disadvantages realized with the RH-OB method and apparatus. The disclosed invention meets those needs by providing a barrel-type degasser having a single substantially continuous diameter opening which avoids the need for two snorkels and eliminates the wear which occurs at the complex vessel bottom and snorkel throat sections.